The invention relates to a method and apparatus for varying the spacing of sequential ignition control puses emitted by an ignition pulse transducer.
In order to operate internal combustion engines with fuel-air mixtures which have been made so lean that the engine is operating in the vicinity of the lean running limits, it is known to regulate the instant of ignition in accordance with an idling roughness signal in such a way that a degree of quiet idling of the engine is maintained which is considered as barely permissible (German Offenlegungsschrift, i.e., laid-open application No. 25 10 526 which corresponds to U.S. Pat. No. 4,178,891.
Apparatuses for obtaining an engine roughness signal are also known in which a phase control circuit is used, with the aid of which an average constant rpm is formed from the actual rpm representing the degree of engine roughness, and the engine roughness signal is generated from the phase difference between the two rpm (German Offenlegungsschrift, i.e., laid-open application No. 24 34 743 which corresponds to U.S. Pat. No. 4,153,013).
It is also known, in order to vary the instant of injection over the entire operational range of an engine, to provide a phase delay circuit located between a voltage-controlled oscillator and the phase comparison circuit of a phase control circuit; the delay period of this phase delay circuit is then variable in accordance with operating parameters of the engine. In this arrangement, the signal emitted by an ignition angle transducer is present at the input of the phase comparison circuit, and is delivered to the ignition device of the engine via the voltage-controlled oscillator. However, with this apparatus only a phase advance of the control signal picked up at the voltage-controlled oscillator, compared with the control signal emitted by the ignition angle transducer, can be obtained (German Offenlegungsschrift laid-open application No. 27 08 245).